The present invention relates to a blower structure for an automotive air conditioner or the like and, more particularly, to a scroll casing structure effective to reduce noise from this type of blower.
This invention can widely be applied to blowers for home use, for use in office machines, for cooling electronic computers and for other purposes, requiring low noise performance, as well as to blowers for automotive air conditioners.
A conventional blower, such as that disclosed in Japanese Unexamined Utility Model Publication No. 48-63305, is formed of a fan, a scroll casing in which the fan is housed, and a motor for driving and rotating the fan. This blower structure is such that air is drawn from one side of the fan and blown in the radial direction of the fan. The scroll casing has a function of gradually restoring a dynamic pressure generated by the rotation of the fan to a static pressure in the scroll casing. In an automotive air conditioner, such as that disclosed in Japanese Unexamined Utility Model Publication No. 57-24566, an inside/outside air changing box has been divided for indirectly reducing various kinds of radiated noise. An, an example of means for reducing noise comprises a sound absorbing member formed of a combination of a porous elastic member and a non-porous elastic member and secured to a surface of the porous elastic member to a surface of the porous elastic member to a scroll casing, as disclosed in Japanese Unexamined Patent Publication No. 63-90415.
The prior art disclosed in the above mentioned Japanese Unexamined Utility Model Publication 48-63305 has a considerably high level of noises from the entire blower, such as air pulsation noise generated from the fan, noise of generation of vortices by separation, generation of a turbulent flow in the scroll casing, and the like. In the automotive air conditioner such as that disclosed in above mentioned Japanese Unexamined Utility Model Publication No. 57-24566, since the inside/outside air changing box is deviced for improvements with respect to these problems, with a result that restrictions are added in respect of vehicle mount conditions and the structure of the inside/outside air changing box is complicated, so that the provision of a low-priced automotive air conditioner improved performance over a wide variety of uses has not been achieved.
With respect to noise reduction based on the sound absorbing member attached to the scroll casing as described in the above mentioned Japanese Unexamined Patent Publication No. 63-90415, a soft polyurethane foam ordinarily used as a sound absorbing material has a high sound absorbing effect with respect to high frequencies above 1000 Hz but has a low effect with respect to frequencies below 1000 Hz. The example disclosed in Japanese Unexamined Patent Publication No. 63-90415 employs a sound absorbing member consisting of two kinds of sound absorbing members attached to each other to absorb vibrational energy of sound waves of a wide range of frequencies to solve the above-described problem, but other problems described below are encountered. If such a sound absorbing member is used, for example vibrational energy of sound waves of low frequencies can be absorbed because a porous material is used as a surface layer, but sound waves cannot reach an inner layer and are, adversely, reflected, so that the effect of a porous elastic material provided on the inner layer is not sufficiently exhibited. In this case, eyed an effect equal to that of a porous elastic material alone cannot be achieved and high-frequency sound is not reduced. Further, if the operation of attaching the sound absorbing member to the scroll casing is performed over the entire inner wall surfaces of the scroll casing in an attempt to optimize the utilization of the effect, an operation to attach the sound absorbing member to a curved surface is included but the attachment process cannot be completed easily, resulting an increase in the cost. Also, there is a need for preventing separation of the sound absorbing member because it is in contact with an air passage surface.
An object of the present invention is to solve these problems and to provide a blower of this kind having a muffling effect over a wide range from low frequencies to high frequencies and thus capable of reducing noise.
The above object is achieved by forming a part of a scroll casing for holding a motor body, constructing the scroll casing by this motor-side scroll casing part and a bell-mouth-side scroll casing part in which a bell mouth is formed, providing a porous member in the form of a flat plate at a position where these two casing parts abut against each other, and constructing a muffling mechanism by the flat-plate porous member and an air layer defined between the flat-plate porous member and the bell-mouthside casing part.
With the above-described structure in accordance with the present invention, sound waves of mixed noises, such as air pulsation noise generated in the upper scroll casing having the flat-plate porous member as a blower bottom wall, vortex noise caused by separation from the blades with the rotation of the fan, and turbulent flow noise in the casing and the like pass through the porous member, so that the sound waves are reduced in medium and high-frequency ranges. Further, the sound waves reach a lower scroll casing inner wall formed of an air layer defined by the flat-plate porous member and the housing and are reflected to interfere with each other in the air layer, so that low frequency range sound is also reduced.
The above and other objects, features and advantages of the present invention will be made more apparent by the following description with reference to the accompanying drawings.